The long term goal of this proposal is to examine the chemical dynamics, mechanisms and kinetics of the ground and excited state reactions of a variety of atmospherically relevant species, with particular emphasis on nitrosyl halides and ozone. It is well established that long term exposure to ozone, nitrogen oxides and other atmospheric pollutants leads to various degrees of lung damage. Loss of ozone in the stratosphere results in increased levels of solar ultraviolet light reaching the Earth's surface, which is expected to cause a higher incidence of skin cancer in humans and significant climatic changes. Several aspects of the reactions of ozone and nitrosyl halides will be investigated. These include vibrationally induced bimolecular reactions, thermal, and photochemical reactions. The reactions will be investigated in both cryogenic matrices, an environment which is useful for trapping reaction intermediates, and in the gas phase. Fourier Transform Infrared and UV-Vis spectroscopy will be used to follow the reactions, providing information on products, mechanisms and kinetics. Of particular interest is the attempt to synthesize oxirene by the photolysis of ozone-alkyne matrices. Oxirene intermediates have been postulated in several biochemically relevant reactions such as the deactivation of aromatase, the enzyme that catalyzes the conversion of androgen to estrogen. Using the matrix isolation technique will hopefully assist in trapping the highly reactive oxirene intermediate.